Analogue-sequencer

> Pretty sure I don't have a loop. Only midi in is connected.

The other possibility is that there is no gap between one block and the
next.
It takes a few milliseconds to decode the received block, so another block
following right away might cause a problem.
What are you using to send the dump ?

Mail me the .syx file privately and I can check it out here.

Cheers,
Colin f